The invention pertains to a coated cutting tool, and in particular, to a cutting tool with a ceramic or polycrystalline cubic boron nitride (PCBN) substrate wherein the coating is applied by a physical vapor deposition (PVD) technique. More particularly, the invention pertains to a cutting tool with a ceramic or polycrystalline cubic boron nitride (PCBN) substrate wherein the coating is applied by a physical vapor deposition (PVD) technique, but prior to the application of the PVD coating scheme, a base coating scheme is applied by chemical vapor deposition (CVD) to the surface of the substrate.
Heretofore, a combination of CVD coating techniques and PVD coating techniques has been used to coat articles. For example, in the context of a cutting tool, U.S. Pat. No. 5,250,367 to Santhanam et al. pertains to a cemented carbide substrate that has a coating scheme thereon. The coating scheme has a CVD coating region on the substrate and a PVD coating on the CVD coating scheme. U.S. Patent Application Publication No. US 2011/0176878 A1 to Nomura discloses a drill head that contains hard cutting tips brazed to the drill head. The cutting tips have a CVD coating region on the cutting tip and a PVD coating on the CVD coating scheme. U.S. Pat. No. 6,599,062 to Oles discloses a polycrystalline boron nitride substrate for a cutting tool. The coating scheme is generally described at Col. 2, lines 16-37, which reads:                This need is met by the coated cutting tool and method of the present invention which are useful for hard turning. The cutting tool of the present invention includes a blank/substrate of polycrystalline cubic boron nitride having a rake surface roughness of no more than about 8 to 10 microinches R.sub.a, having a refractory hard coating containing aluminum applied thereto by one of a CVD or PVD technique or combination thereof. Preferably, the coating includes a titanium aluminum nitride layer (e.g., TiAlN) deposited onto the substrate via a PVD technique in a thickness of at least 2 micrometers, and preferably about 2 to 5 micrometers, and more preferably about 3 micrometers in thickness. The PCBN preferably includes at least 40 vol % CBN in addition to the binder.        The coating may alternatively include a lower layer of aluminum oxide (e.g., Al2O3), deposited with or without underlayers of TiN, TiC, TiCN, TiAlN, TiOCN between it and the substrate, and optionally, with an outer layer, for example, of titanium nitride (TiN). A primary function of the outer layer is to act as a visual wear indicator for the machine operator. This layer is typically lighter colored than the substrate of the tool insert.PCT International Publication No. WO 2008/008207 A2 to Inspektor et al. discloses a cutting tool that has an anodized top coating layer. A general description of the pre-anodized cutting tool is at Paragraphs [0029][0031], which read:        [0029] Referring to the specific embodiment illustrated in FIGS. 3A, 3B and 3C, FIG. 3A shows a pre-anodized cutting tool (generally designated as 30) with a pre-anodizable coating scheme (bracket 32) thereon. In this regard, the pre-anodized cutting tool 30 comprises a substrate 34 that has at least one surface 36. While the substrate 34 may vary in composition depending upon the application, the material for the substrate can be selected from the group comprising cemented carbides (e.g., cobalt cemented tungsten carbides), ceramics (e.g., SiAlON's) and cermets (titanium carbonitride-based materials) and high speed steels).        [0030] The pre-anodizable coating scheme 32 includes an underlayer coating arrangement shown by brackets 40. The underlayer coating arrangement 40 may take on any one of many different coating architectures. It may comprise a single coating layer or it may comprise a plurality of coating layers possibly in a periodic sequence or not in a periodic sequence. The thicknesses of the various coating layer(s) in the underlayer coating arrangement 40 can also vary depending upon the specific application.        [0031] The method to apply the coating underlayer arrangement 40 may also vary depending upon the application wherein the method may include physical vapor deposition, chemical vapor deposition, and various variations or modifications or combinations thereof known to those of ordinary skill in the art. Exemplary coating arrangements that could serve as the underlayer coating arrangement 40 are shown and described in the following U.S. Pat. No. 5,864,297 and U.S. Pat. No. 5,858,181 to Jindal et al. for Physical Vapor Deposition of Titanium Nitride on a Nonconductive Substrate, U.S. Pat. No. 5,879,823 to Prizzi et al. for a Coated Cutting Tool, and U.S. Pat. No. 5,364,209 to Santhanam et al. for a Coated Cutting Tools. Each one of these patents is assigned to Kennametal Inc. of Latrobe, Pa. 15650 United States of America, and is hereby incorporated by reference herein.        
The following patent documents pertain to the application of a CVD titanium nitride layer on top of which is applied a PVD coating scheme in the context of electronic components: U.S. Pat. No. 5,300,321 to Nakano et al., U.S. Pat. No. 5,972,179 to Chittipeddi et al., U.S. Pat. No. 6,010,940 to Lee et al., U.S. Pat. No. 6,562,715 to Chen et al., U.S. Patent Application Publication No. US 2001/0004478 to Zhao et al., U.S. Patent Application Publication No. US 2009/0087585 A1 to Lee et al., and PCT International Publication No. WO 02/095808 A1 to Bagley et al.
While the above documents mention PVD coating and CVD coating, there remains a need to provide a PVD-coated ceramic substrate or PVD-coated polycrystalline cubic boron nitride (PcBN) substrate, as well as a method of PVD coating a ceramic substrate or a PcBN substrate. In this regard, ceramic cutting tools and PcBN cutting tools are generally electrically non-conductive. Application of coatings via a PVD technique generally involves the deposition of charged particles onto the surface of the ceramic substrate or the PcBN substrate. Further, the ceramic substrate or the PcBN substrate may need to be pre-treated with a plasma treatment such as etching prior to the PVD coating process. Overall, the low electrical conductivity of the ceramic substrate and the PcBN substrate renders these materials difficult to apply a coating via a PVD technique.
The above difficulty associated with the low electrical conductivity of the ceramic substrate and the PcBN substrate can be overcome by the application via a chemical vapor deposition (CVD) technique of an electrically conducting base coating scheme prior to the application of the PVD coating. There is an advantage associated with the CVD process for a ceramic substrate or a PcBN substrate in that CVD does not require the deposition of charged particles prior to the CVD coating process. A base CVD coating scheme with electrically conductive properties and sufficient thickness (a minimum of 100 nanometers) will enable the use of a PVD coating process to coat the CVD-coated substrate.